You can go to petsmart and buy dog dewormer with fenbendazole. Shrimp will not be effected nor MTS/Pond/Ramshorn but it will likely effect your briggs/nerites, and unsure how long till you can put briggs/nerites back into the tank.
its dog deworming powder. its not intended for a fish tank so if you ask for dewormer for a fish tank they will look at you like you have 2 heads. i got mine at a petsmart, but im sure almost any pet suply store carries it. i'll try to find a picture of the box for you...
If you have a feed store near you they will carry it as well. That is where I got mine. It does not take much in the tank to kill the hydra. Just a very small pinch and when you put it in the tank make sure you turn off the filter and take any AC out of it as it will filter out the meds. After 2 doses you sould do a 50% water change on the tank. This should have no ill effect on the shrimp in the tank.
dont quote me on this but i think its 1 gram per 10 gal. dont forget to break it up cuz its kind of chunky. lay a dollar bill over top of the pile of meds and run a credit card over it to break up the rocks.
I used Joes juice on mine and it worked great. Just thought I would chime in. it comes with a syringe and you suck up the stuff and squirt it over the anemones. Its for salt water pest anemones but it works since it was the only thing I had. I had nerites snails in the tank and yellow shrimp.